Ammonium nitrate explosive compositions containing (metal-excess chloride) combustion catalyst



A. KEENAN ETAL 3,336,171

AMMONIUM NITRATE EXPLOSIVE COMPOSITIONS CONTAINING Aug. 15, 1967 I (METAL-EXCESS CHLORIDE) COMBUSTION CATALYST Filed Feb. 11, 1966 2 Sheets-Sheet l 52 9 m2o z 560 .10 mo 05E OOM O Y N c K mmm E ,R W EZF KT mm WJL HL TRC Z mmw m. NIIIH ATTORNEYS TEMPERATURE- c N Aug.

Filed Feb. 11. 1966 15, 1 67 A. e. KEENAN ETAL AMMONIUM NITRATE EXPLOSIVE COMPOSITIONS CONTAINING (METAL-EXCESS CHLQRIDE) COMBUSTION CATALYST 2 Sheets-Sheet 2 I I 40 I60 INVENTOR E- ARTHUR 3. KEENAN KARL J NOTZJR v 5' NICHOLAS B.FRANCO ATTORNEY}? United States Patent 3,336,171 AMMONIUM NITRATIE EXPLOSIVE CGMPOSI- TlONS CONTAINING (METAL-EXCESS CHLO- RIDE) COMBUSTION CATALYST Arthur G. Keenan, Miami, Fla., Karl J. Notz, Jr., Oak Ridge, Tenn., and Nicholas B. Franco, Coral Gables, Fla, assignors to Research Corporation, New York, N.Y., a nonprofit corporation of New York Filed Feb. 11, 1966, Ser. No. 526,818 5 Claims. (Cl. 14943) ABSTRACT OF THE DISCLOSURE An explosive composition containing ammonium nitrate, at least 0.05% by Weight of a metal and at least one chloride anion per metal atom in excess of the ratio of chloride anion to metal atom that would be obtained by adding the metal as its chloride salt.

This invention relates to ammonium nitrate gas producing or explosive compositions, and more particularly to ammonium nitrate compositions having an improved decomposition rate.

Ammonium nitrate is widely used as a component of explosive compositions often in admixture with an oxidizable material such as cellulose or related materials, various other polysaccharides, carbohydrates and oxidizable organic compounds, and carbon and sulphur. Various primers or detonators such as nitr-osta-rch, nitrocellulose, nitroglycerine and trinitrotoluene may also be included in these compositions.

Another approach utilized for improving the sensitivity of an ammonium nitrate explosive is the incorporation of a combustion catalyst into the explosive composition. The most commonly employed combustion catalysts contain chromium usually in the form of chromate or other readily available salts of chromium. Compositions containing iron, nickel and cobalt have been described for use in conjunction with chromium. Other compositions containing various metals have also been described as combustion catalysts.

We have discovered that this combustion catalyst effect of metals and metal salts is greatly improved by using the metal or salt in conjunction With a stoichiometric excess of chloride anions.

It is, therefore, the principal object of the present invention to provide ammonium nitrate gas producing or explosive compositions having improved decomposition rates.

The present invention is an ammonium nitrate gas producing or explosive composition containing at least 0.05% by weight of a metal and at least one chloride anion per metal atom in excess of the ratio of chloride anion to metal atom that would be obtained by adding the metal as its chloride salt.

The metal may be supplied in free or combined form. For reasons of convenience and economy, it is preferred to employ a readily available salt containing the metal as a cation or as part of the anion. A list of such suitable salts would include nitrates, carbonates, sulfates, chromates and the like. There is no particular advantage to be derived in using the free metals since their conventional salts are usually available at a lesser cost. It is noted that the ammonium nitrate melt dissolves most metals by forming the metal nitrate.

The decomposition rate of ammonium nitrate gas producing or explosive compositions, as measured by timetemperature studies, is improved by the incorporation of at least 0.05% of a metal usually provided as its salt and excess chloride anion as described more fully below.

The improved catalytic effect of the present invention increases with increasing the metal content of the explosive composition until either the diluent effect of the metal salt or its limited solubility in the system begins to decrease its effectiveness. These factors vary widely With the particular metal salt employed and there is no theoretical upper limit for the amount of metal which may be employed. Satisfactory explosive compositions containing as high as 20% by Weight of the metal have been prepared and tested. Compositions containing about 1 to 5% by weight of the metal would be the most useful.

As stated above, ammonium nitrate compositions containing at least one chloride anion per metal atom in excess of the ratio obtained by adding the metal as chloride exhibit the improvement of the present invention. The rate of decomposition increases markedly as the ratio of chloride anions to metal atoms increases up to about 10:1 and relatively little further improvement, and possibly some decrease, is noted as additional chloride is added. Data illustrating this is presented in graphical form in FIG. 1 wherein the maximum temperature obtained on decomposing ammonium nitrate containing 0.1% by weight of a metal is plotted as a function of the amount of chloride anions present. In this experiment the particular metal employed was copper added as its carbonate; generally speaking other metals and metal salts behave in a similar manner.

The rate of improvement obtained using metal-chloride combustion catalysts in an ammonium nitrate composition according to the present invention with various metals was determined. In order of decreasing effectiveness, the metals are:

Chromium Titanium Copper Lead Silver Manganese Nickel Mercury Iron Bismuth Gold Platinum Palladium Zinc Cobalt Cadmium Cerium Aluminum Zirconium Chromium, copper, silver and nickel are particularly effective. Metals having a standard oxidation potential above 2.0 volts, i.e., the alkali metals such as lithium, potassium, sodium, et cetera, are much less effective.

Chloride ion is by far the most effective halide for use in conjunction with metals in the synergistic catalytic combinations of the present invention. A slight beneficial effect has been noted when bromide is used in place of chloride, but this effect is not of practical interest when considered in the light of the relative cost of bromide salts and chloride salts. The substitution of iodide or fluoride for chloride does not give any appreciable synergistic effect. The particular cation employed as the chloride carrier is not critical, but for reasons of economy and convenience, the chlorides of sodium, potassium and ammonium are preferred.

The improved compositions of the present invention are made by incorporating the metal containing additive and the chloride anion containing additive into an ammonium nitrate explosive composition by any conventional means, for example, by milling or dry mixing the ingredients. The mixture may then be shaped or pressed or otherwise prilled to the form of compacted grains. Regular shaped particles are preferably prepared by adding the ingredients to each other in a fused or molten condition and pressing the resultant paste into suitable molds. The particles are allowed to cool before being removed from the mold.

The term ammonium nitrate as used herein is intended to include ordinary commercial grade ammonium nitrate,

military grade ammonium nitrate or mixtures of inorganic nitrates and ammonium nitrates wherein ammonium nitrate is the preponderant nitrate. Such compositions may contain a small amount of impurities and are generally provided with a small amount of moisture resisting material such as petrolatum or paraffin.

Our invention is further illustrated by means of the following non-limiting examples:

The shortening of the induction period and the improved decomposition of ammonium nitrate explosive compositions, according to the present invention, were demonstrated by thermographic analysis. Compositions containing ammonium nitrate alone, ammonium nitrate containing 5 mole percent of sodium chloride as the sole additive, ammonium nitrate containing a metal salt as the sole additive, and ammonium nitrate containing both sodium chloride and a metal salt (chloride to metal atom ratio of 37:1) as additives.

The curves shown in FIG. 2 of the drawing are graphs of temperature against time obtained on a potentiometric recorder from a thermocouple set in an ammonium nitrate sample held in a furnace at 185 C. The method employed for measuring temperature was generally similar to that used in standard differential thermal analysis. Since the temperature differentials obtained were rather large, it was not necessary to utilize certain of the refinements of conventional differential thermal analysis. The thermocouple reference junction was located in a constant temperature ice bath rather than in an inert sample in the furnace itself, and the furnace was programmed to maintain a constant temperature of 185 rather than rise continually. None of these variations made any essential difference in the results obtained since more refined procedures would show exactly the same relative behavior for the various systems studied.

In a very careful series of experiments, prilled ammonium nitrate dried at 110 C. for several days and sodium chloride and metal salts dried at 100 for about 30 minutes were employed. The reaction tube was flushed with dry nitrogen and, after the system had melted, the melt was flushed with nitrogen at 185 until ready to start the run. However, it was shown in separate experiments that the thermal peaks obtained were not dependent on these refinements and that the same results are obtained with ordinary air-dried chemicals without nitrogen flushing. Particle size, grinding and mixing are not critical factors since the system melts before reacting.

The particular thermographs shown in FIG. 2 were obtained by weighing six grams of air-dried ammonium nitrate and the required amounts of other constituents into a glass reactor tube, shaking to achieve some degree of mixing and inserting the tube into a furnace at 185 C. The sample melted circa 160170 depending on the particular composition being tested, reached 185 in about 30 minutes total time and took off in another to minutes, again depending on the composition being tested. These parameters apply to the particular apparatus and conditions, especially the furnace temperature, employed. In general, thermographic methods give only relative results, the absolute values of which are dependent on the specific apparatus and operating parameters. However, the relative behavior of the samples in a given system remains the same.

In the drawing, curve A shows the results obtained using ammonium nitrate alone without any additives and confirms the relative insensitivity of pure ammonium nitrate. Curve B shows the relatively small improvement obtained using only a metal additive (about 0.1% by weight added as its salt; the particular metal employed Was chromium but other metals give similar results). Curve C shows the improvement obtained by using 5 mole percent sodium chloride as the sole additive. Curves D, E, F and G show the synengistic improvement obtained when compounds of chromium, copper, silver and nickel, respectively, are used as additives together with sodium chloride in a chloride/metal atom ratio of 37:1. The more active the metal, the shorter the induction period and the higher the peak obtained.

In order to show the effect of increasing metal concentration at a constant chloride content, a rate run was made at 185.5 C. in which varying amounts of silver nitrate were added to a charge containing 7 grams of ammonium nitrate and 570 milligrams of sodium chloride. The chloride content was kept constant at a mole ratio of ammonium nitrate to sodium chloride of 9, and the silver nitrate was varied between 0.016 and 0.71 mole percent. The results are tabulated in the table below, which lists the maximum rate of gas evolution and the induction period (I.P.) taken as the time interval between ze-ro time and the occurrence of the rate maxi-mum.

Silver Nitrate Mole Percent LP. (min) Max. Rate Added (mg) Silver Nitrate (ed/min.)

None 0. 00 63. 1 24. 6 2. 7 0. 016 59. 1 42. 3 4. 6 0. 02s 59. 5 44. 1 13. 5 0.081 59. 1 50. 0 26. 0 0.16 58. 2 54. 6 31. 7 0. 19 58. 3 55. 0 11s. 3 0. 71 58.2 51. 7

It is apparent that various changes may be made in the compositions described herein without departing from the scope of the present invention.

We claim:

1. An explosive composition consisting essentially of ammonium nitrate, at least 0.05% by weight of a metal and at least one chloride anion per metal atom in excess of the ratio of chloride anion to metal atom that would be obtained by adding the metal as its chloride salt.

2. A composition according to claim 1 wherein the metal is chromium, copper, silver or nickel.

3. A composition according to claim 1 wherein the metal is in the form of salt.

4. A composition according to claim 1 containing at least ten chloride anions per metal atom.

5. A composition according to claim 1 containing 1 to 5% by weight of a metal.

References Cited UNITED STATES PATENTS 2,154,416 4/1939 Tyre 149--46 2,548,693 4/1951 Whetstone et al. 149-46 X 2,816,012 12/1957 Walton 14943 X 2,829,958 4/1958 Davidson et al. 14943 X FOREIGN PATENTS 160,978 2/ 1955 Australia. 528,513 7/1956 Canada.

CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner.

S. J. LECHERT, 5a., Assistant Examiner. 

1. AN EXPLOSVIE COMPOSITION CONSISTING ESSENTIALLY FO AMMONIUM NITRATE, AT LEAST 0.05% BY WEIGHT OF A METAL AND AT LEAST ONE CHLORIDE ANION PER METAL ATOM IN EXCESS OF THE RATIO OF CHLORIDE ANION TO METAL ATOM THAT WOULD BE OBTAINED BY ADDING THE METAL AS ITS CHLORIDE SALT. 